EP3305947A1 - Melting method during floating-zone growth of silicon - Google Patents

Melting method during floating-zone growth of silicon Download PDF

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Publication number
EP3305947A1
EP3305947A1 EP16724471.4A EP16724471A EP3305947A1 EP 3305947 A1 EP3305947 A1 EP 3305947A1 EP 16724471 A EP16724471 A EP 16724471A EP 3305947 A1 EP3305947 A1 EP 3305947A1
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EP
European Patent Office
Prior art keywords
silicon
rod
diameter
container
melt
Prior art date
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Application number
EP16724471.4A
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German (de)
English (en)
French (fr)
Inventor
Anatoly KRAVTSOV
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Individual
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Individual
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Publication date
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Publication of EP3305947A1 publication Critical patent/EP3305947A1/en
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/06—Silicon
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
    • C30B15/14—Heating of the melt or the crystallised materials

Definitions

  • the invention relates to the production of silicon, for example, for the power microelectronics or the photoelectric industry including the manufacturing of solar cells.
  • the purpose of this production is obtaining dislocation-free silicon single-crystals from the source rods of relevant quality.
  • the process of obtaining silicon single-crystals using a float-zone melting method includes two important stages: obtaining the source rod of specified dimensions with the required properties and vertical (predominantly induction) float-zone melting.
  • the source rod fit for growing dislocation-free single-crystals is obtained by depositing from the gas phase during the silane decomposition process in hydrogen or by growing from the melt.
  • the source rod must have the impurity content requested by the customer, a cylindrical shape with minimal ellipticity - the difference between the diameters of an ellipse in the rod's cross-section (less than 5 mm) and camber - less than acceptable value (usually 5 mm/metre of length), a smooth surface and dimensions equal or almost equal to the size of the desired single crystal.
  • the rod should be free of cracks.
  • melt droplets are formed on the melting surface and do not flow down into the zone ( Figure 4 ). These melt droplets have a considerable volume and may cause spillage of the melt zone upon entering.
  • the source rod with a diameter of several millimetres is heated by channelling current through it. The heat dissipation occurs from the surface of the growing rod. Due to heating from the neighbouring rods, the heat dissipation isn't uniform and thermomechanical tensions are formed within the rod and grow with increasing diameters of the rods. As a result, with the increase of diameter of the rods the task of ensuring the absence of cracks in them becomes more difficult.
  • the rods obtained by deposition from the gas phase can be improved by prior passing of the molten zone in a vacuum with obtaining a polycrystalline rod without ellipticity, sagging, with a smooth surface and diameter close to one necessary for growing single-crystals.
  • the requirements to the source rod prior to the preliminary passing of the zone in a vacuum are toned down insignificantly and the presence of the cracks in the rod and its dimensions close to the requested for single-crystals is preserved. It is important that despite the shortcomings, silicon with the lowest content of impurities can be obtained exactly by deposition from the gas phase.
  • the rods can be obtained without using heating from the graphite via the crucible, but through applying inductive or electron-beam heating inside the volume of the processed silicon.
  • Ciszek GROWTH OF 40 mm DIAMETER SILICON CRYSTALS BY A PEDESTAL TECHNIQUE USING ELECTRON BEAM HEATING", published in "Journal of crystal growth" No. 12 (1972), page 281-287 [8].
  • the effect occurs with various diameters, but does not provide the possibility of growing crystals of a diameter exceeding 50-150 mm.
  • these methods do not specify the required properties of the grown crystals for optimisation of the subsequent float-zone melting process.
  • the closest to the method proposed shall be a method in accordance with patent application No. EP0142666 [9] regarding the production of single-crystal silicon by the float-zone melting method using the source rods with a diameter that differs from the source rod by no more than 20%, obtained in the process of gas-phase growing at low growth rates or from the melt by the way of two-stage process of float-zone melting or growing of the source rod from the polysilicon lumps using the Czochralski method.
  • the disadvantages of the gas-phase deposition process as described in the application No. EP0142666 are following: buildups in the form of surface irregularities, deviations from the cylindrical shape and thermomechanical tensions, which in turn lead to rod cracking as their diameter increase.
  • the cultivation of the rods utilising the Czochralski method finds expanding applications for growing the single-crystals with a diameter of 200 mm by using the float-zone melting method, as reflected even in the promotional materials of some companies, such as CFZ silicon of the Chinese company Tianjin Zhonghuan Semiconductor Co., Ltd ( http: // en.tjsemi.com / main / productdetails _ s _ 1.aspx ).
  • a source rod is grown using the Czochralski method and a dislocation-free single-crystal is grown using the induction float-zone melting method.
  • the disadvantage of this method is the impossibility to obtaining silicon with the resistance of more than 50 Ohm*cm due to impurities introduced in the melt from the crucible and graphite heater in the course of a standard process and an uncompetitive costs of applying the Czochralski method with the magnetic field.
  • the process does not allow to recycle waste with low specific resistance (less than 0.1 Ohm*cm) for later use in solar energy.
  • the goal of the invention is to obtain silicon in the form of high-purity rods made of source silicon of varying quality and forms, suitable by their electrical, mechanical and geometrical properties for growing single-crystals of various purposes using the float-zone melting method.
  • the source rod for growing of the single-crystal using the float-zone melting method is obtained by pulling the seed from the melt utilising electron-beam heating. Electron-beam heating occurs directly inside the container with silicon without the use of graphite and heat transfer through the walls of the container, thus preventing the main sources of impurities from contaminating the melt. Additionally, silicon with purity corresponding to quality requirements for the single crystals to be grown by float-zone melting method is used as a source raw material.
  • the technical result is achieved by the fact that in the production of the silicon single-crystals utilising float-zone melting method, which includes growing of the source rod by seeded pulling it from the melt, silicon is heated inside the container by minimum of two electronic beams to reduce or eliminate interaction of the melt with the container.
  • the focal heating spots made by electron beams move along the arcs of the specified radius not less than the diameter of the grown rod, in total corresponding to the central angle of not less than 340 degrees.
  • high-quality polycrystalline silicon or silicon residues formed after cutting of the single-crystals by float-zone melting method are used as source raw materials. During the process, any contact of the melt with the container from which the rod is to be grown is prevented.
  • a container with a diameter of not less than 5 diameters of the grown rod is used, at the same time the entire process is carried out by applying 0.03-0.06 kW/cm 2 of power to the melt starting from the melting procedure until the end of rod growing.
  • the motion path of focal spots can be selected by setting such a diameter that the distribution of temperature in the melt will provide stable growth of the crystal with a set tapered shape followed by a cylindrical shape while a container wall temperature remains low, including such case when the inner surface of the container has a layer of unmelted source silicon with a thickness of 5-20 mm.
  • the container diameter should be not less than 5 diameters of the grown source crystal.
  • the method is implemented as follows: silicon is placed in a container containing a thermal insulator (1) and a cooled device (2). Then the container is placed into the melting chamber of the apparatus with subsequent creation of a vacuum followed by melting utilising electron-beam heating (3). At the same time, the rays are spread to a specified diameter and scanning is started, forming a ring heating zone (4).
  • the diameter of the focal spot heating ⁇ moving zone (5) is chosen in such a way as to achieve the desired result - to melt the entire silicon in the container or preserve a part of the unmelted original bed (7) between the molten zone (6) and container walls.
  • a seed crystal (8) is placed into the container; it contacts the melt and grown into a rod (9) of the required diameter.
  • the growing process is controlled by modifying the speed of pulling (V) and intensity of heating (3), while ensuring the constant diameter of the ring heating (3) zone (4).
  • Scan trajectories of the electron beam focal spots (5) together form the shape of a ring close to the ring of the required diameter and form the thermal field of a thermal symmetry sufficient for growing a cylindrical rod (9).
  • a container with an internal diameter 420 mm is stacked with polycrystalline silicon.
  • the container is placed in a vacuum chamber of the device.
  • the power supplied is set to 1.2-1.3 kW per 1 kg of loaded silicon and electron beam scan mode is enabled along the arcs of a circle of 250-300 mm with periodic decrease of circle diameter to 50-100 mm.
  • scanning of focal spots made by electron beams is continued for 20-60 minutes ensuring the maximum radii of arcs, while at the same time providing retention of a layer of unmelted source silicon 5-20 mm thick on the inner surface of the container.
  • the supplied power is reduced by 20-50% and the seed crystal is introduced to the point when it contacts the melt followed by choosing the power optimal for growing.
  • Further process is lead similar to the processes of growing from the crucible utilising the Czochralski method; for that purpose, the radii of the arcs formed by the moving focal spots are gradually increased up to a value not less than the diameter of the grown crystal and fixed afterwards.
  • the central angle of arc coverage is not less than 340 circular degrees in total.
  • the rod of 75 mm in diameter is grown with variable speed, starting with a rate of 2.5 mm/min and finishing at less than 2 mm/min, additionally the rod is rotated with a frequency of 10-15 rpm while the container remains stationary.
  • the power applied to the melt is reduced from 60 to 40 kilowatts from 2 heaters in total as the crystal grows.
  • the grown rod is cooled down, removed from the chamber of the vacuum device and its geometrical and electrophysical parameters are evaluated for their compliance with the parameters required to obtain a single-crystal. In these processes, specific electrical resistivity of the grown rod is acceptable and complies with reference parameters of loaded polycrystalline silicon.
  • the rod is prepared for the growing process; it can be treated mechanically and chemically, if necessary. After that, the rod is placed into the induction float-zone melting plant and a dislocation-free single-crystal is grown, which diameter differs from the diameter of the grown rod by no more than 20%. For this example, a single crystal of 65 mm in diameter was grown.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Silicon Compounds (AREA)
EP16724471.4A 2015-05-26 2016-04-20 Melting method during floating-zone growth of silicon Withdrawn EP3305947A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
LVP-15-48A LV15065B (lv) 2015-05-26 2015-05-26 Silīcija beztīģeļa zonas kausēšanas paņēmiens
PCT/IB2016/052236 WO2016189402A1 (ru) 2015-05-26 2016-04-20 Способ плавки при зонном выращивании кремния

Publications (1)

Publication Number Publication Date
EP3305947A1 true EP3305947A1 (en) 2018-04-11

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EP16724471.4A Withdrawn EP3305947A1 (en) 2015-05-26 2016-04-20 Melting method during floating-zone growth of silicon

Country Status (4)

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EP (1) EP3305947A1 (lv)
IL (1) IL255889A (lv)
LV (1) LV15065B (lv)
WO (1) WO2016189402A1 (lv)

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4323793A1 (de) * 1993-07-15 1995-01-19 Wacker Chemitronic Verfahren zur Herstellung von Stäben oder Blöcken aus beim Erstarren sich ausdehnendem Halbleitermaterial durch Kristallisieren einer aus Granulat erzeugten Schmelze sowie Vorrichtung zu seiner Durchführung
JP5318365B2 (ja) * 2007-04-24 2013-10-16 Ｓｕｍｃｏ Ｔｅｃｈｘｉｖ株式会社 シリコン結晶素材及びこれを用いたｆｚシリコン単結晶の製造方法

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LV15065B (lv) 2015-11-20
WO2016189402A1 (ru) 2016-12-01
LV15065A (lv) 2015-10-20
IL255889A (en) 2018-04-30

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